The ultimate goal of a smoke detector is to quickly detect every fire event and ignore every nuisance event. Virtually all smoke detectors manufactured today fall short of this goal, either because they are slow to activate during certain fire events or unwittingly activate during certain nuisance events. The primary reason is that a fire event produces several distinct signatures, including smoke, light, heat, humidity, certain gases, and sound, but most smoke detectors are designed to detect only one signature, smoke. Conventional smoke detectors thus generally cannot discriminate between smoke particles and certain nuisance particles, such as dust, steam, or cooking aerosols. This typically forces the smoke detectors to be either insufficiently sensitive, activating very slowly in response to smoke particles, or overly sensitive, activating very quickly (and erroneously) in response to nuisance particles.
Photoelectric smoke detectors operate by illuminating a sampling volume with light from a light emitter and detecting light scattered by any particles in the sampling volume with a light receiver. One technique for photoelectric smoke detectors to better discriminate between smoke particles and nuisance particles is to use two different wavelengths of light. Smoke particles are generally smaller than nuisance particles and will scatter light more efficiently than nuisance particles as the wavelength decreases. Thus, by evaluating the scattering of light by two wavelengths, smoke particles may generally be discriminated from nuisance particles.
While this technique helps to discriminate between smoke particles and nuisance particles, it may not necessarily decrease the time to activate, since smoke still must travel from the fire source to the smoke detector, and, if the sampling volume is located inside the smoke detector, the smoke must also enter the smoke detector and any detection chamber contained therein. Thus, there is a need for smoke detectors with more rapid response times and that reliably distinguish between fire events and nuisance events.